1. Field of the Invention
The present invention relates to an optical scanner device and in particular to an optical scanner device for acquiring data representing a selected plurality of pixels from a transparent image bearing media, said scanner device including a light source, a light sensor, means for inserting said media in an operative position between said light source and said sensor.
2. Prior Art
An optical scanner is a device that uses light to acquire data from an image bearing media and generates and stores electrical signals, in particular in digital form, corresponding to the scanned image; the term "image" is used in its broadest context to include any graphically represented indices, in particular pictures, drawings and text. Scanners can acquire data from different sources, such as sheets, photos, slides, films, and so on. Scanners are used in facsimile machines, photocopying machines, and are now widely used in the data processing field, particularly in multimedia applications; scanners can also be used to convert traditional photos to digital format, for example for use on CD-ROM.
Referring in particular to a scanner for transparent image bearing media, such as slides/transparencies or negatives/films, the image being scanned is illuminated on one side by a light source, typically a fluorescent or incandescent lamp. The light crosses the image and then strikes a light sensor positioned on the opposite side of the transparent media.
The light sensor includes a plurality of photosensitive elements. Each photosensitive element acquires data corresponding to an elemental area of the scanned image (picture element or pixel). The number of pixels acquired, and therefore, given a selected area to be scanned, the distance between two adjacent picture elements, defines the scanner resolution in the raster pattern corresponding to the original image.
The output voltage of each photosensitive element is converted to a digital value. In a bi-level scanner a simple voltage comparator is used to output a black (0) or white (1) level for each photosensitive element. In a gray-scale scanner, an analog to digital converter (ADC) will output a binary bit pattern corresponding to a gray value for each photosensitive element. Depending on the number of bits assigned to each pixel, the scanner will support different shades of gray; a scanner that supports 64 gray levels, for example, outputs a 6-bit binary value, ranging from black (000000) to white (111111).
In a color scanner, the image is illuminated with different color light sources, usually red, green and blue (RGB), as in a conventional gray-scale scanner. Each color light source allows detection of the corresponding color component value for each pixel; the result is the composite RGB color definition of the scanned image. If for example the ADC supports 256 levels (8 bits) of gray for each color, a standard 24-bit RGB color value is generated to represent each color pixel (for 16.7 million possible colors).
Different approaches are used for supporting color on scanners. The basic color-scanner technology uses a white-light source shining through a rotatable RGB filter assembly onto the image being scanned, effectively creating an alternating sequence of red, green and blue light beams. Another approach to support color on scanners uses three separate light sources, red, green and blue, shining in sequence. Yet another approach uses a color-filter assembly separating the white light after crossing the image into its red, green and blue components.
In addition, an infrared light source can be used to implement a surface defect correction operation, to remove scratches, finger-prints, dust and any artifact from the transparent media surface, as described in U.S. Pat. No. 5,266,805.
Typically, the sensor is a CCD (charge-coupled device). A CCD is an integrated circuit that contains a plurality (an array) of tightly packed photosensitive elements; the output voltage of each photosensitive element is proportional to the amount of light striking it.
The common scanner techniques apply a set of lenses (objectives), to focus the image on the light sensor. Usually, a single scan line from the image is focused onto a linear CCD; scanning then advances to the next scan line, by moving either the light sensor or the transparent image bearing media. An optical path required for correct focusing results in a bulky assembly. Mirrors are often used to reduce the size of the device, implementing a sophisticated folded optical path scheme. In addition to the complicated optical path, optical aberrations may result which need to be corrected for optimum imaging. Several products implementing the above mentioned technology are available on the market by photographic companies, such as Vision 35 by AGFA, RFS 2035 by Kodak, CoolScan by Nikon, SprintScan 35 by Polaroid.
Optical fiber lenses are used in scanners for non-transparent media (e.g., photocopying machines), as described in U.S. Pat. No. 4,559,564. This features a photo-sensitive plate including a light source and a layer of light sensors (MOS or CCD), with on top a carrier holding optical fiber lenses and a glass protection.
A hybrid image sensor board is also known in the same field, as described in "A novel contact image sensor (CIS) module for compact and lightweight full page scanner applications"--Anderson, E. E., Weng Lyang Wang--Proceeding of the SPIE--The International Society for Optical Engineering, Vol. 1901, 1993, pages 173-181. The board (18 mm in thickness) includes a light sensor array, a LED array light source, one to one rod lenses and a cover glass.
A scanner usually has some physical link to a computer for transferring scanned image information to it. Typically, known scanners include a special interface card that plugs into an expansion slot or a SCSI connector. Digital data corresponding to the scanned images transmitted to the computer are then usually stored on disk in a standard file format, most commonly TIFF; that allows for example users to easily capture graphical images, that can be then incorporated into documents.
There are some drawbacks with this prior art. Known scanners, using a set of lenses or equivalent means to focus the image on light sensors, are bulky, cumbersome and desktop oriented; a need exists for a scanner that is small, lightweight, compact and portable. Light sensors used in the prior art are unacceptable because all of them include a protection glass on the photosensitive elements that does not allow said photosensitive elements to be in direct-contact with the transparent media; the photosensitive elements are too far from the protection glass (and consequently from the transparent image bearing media) to ensure good focusing without lenses.
Particularly, portable computers usually offer two slots that are a bus expansion for plugging small size credit-card boards. A common standard communications format for these PC cards is that established by the Personal Computer Memory Card International Association (PCMCIA); some multimedia PCMCIA cards are already available on the market (e.g. for an audio feature). All the scanners known in the art are too large to fit into a PCMCIA box and such format, in particular PCMCIA type III format (85.6 mm in length, 54.0 mm in width and 10.5 mm in thickness) has never been used in similar devices because of physical constraints. In addition, techniques known in the prior art are complex and associated costs of implementation are high, so that available scanners on the market are quite expensive; the cost grows as resolution increases, while lenses are a fixed significant cost. No low-cost scanner exists in the above mentioned format.
The above drawbacks and limitations of the prior art are overcome by the present invention as described and claimed.